This
document provides a glossary of measurements and presented data relevant to
Fugro Meteorological & Oceanographic (MetOcean) Monitoring Systems.
The details and capabilities of the sensors of any particular system are
separately documented. This is a generic document for all Fugro GEOS
MetOcean systems: most systems will comprise a subset of the measured and
calculated parameters described below. Please contact Venturer | .support@fugro.com
if you require any additional functionality for an existing deployed system.

The numeric mean of wind speed measurements recorded during the measurement period. Wind speed measurements are received from the measuring instrument at 2Hz or 4Hz according to client specifications. For moving installations, eg. ships, wind speed is corrected according to the vessel’s course and speed.

The
highest value of a 3-second rolling mean of recorded wind speed during the
measurement period.

Wind
Direction:

The
numeric mean of measured wind directions recorded during the preceding
measurement interval. The reported value is a bearing (in degrees) with
respect to true north that identifies the source of the wind driven airflow.
For moving installations, e.g. ships, wind direction is corrected for vessel
course, speed and heading. For floating stationary systems, wind direction is
corrected for vessel heading.

Selected
Wind Sensor:

For
systems fitted with multiple wind sensors a diversity system is configured to
maximise reported data quality for all angles of incident wind. This is a
text display identifying the current sensor providing wind speed and
direction measurements.
Dependent
on the relative positioning of multiple wind sensors, the diversity system
can be configured to present wind speed and direction data from the sensor
with the highest measured speed, or can be configured to present data from a
particular sensor based on a look-up list of wind direction sectors.

Notes:

It
is usual for Fugro GEOS Meteorological / oceanographic monitoring to present
wind speed data in knots. Logging and display of data in other units can be
configured on request. The units of displayed values are always shown within
the web page data displays.

Wind Severity Index (WSI)

A parameter used within helideck monitoring systems - equal to a rolling 10-minute mean value of wind speed corrected[1] from the elevation of measurements to an elevation 3m above the helideck surface.

The
numeric mean of air temperature measurements recorded by a standard
thermometer during the measurement period. Unless otherwise specified by the
client, the Fugro GEOS WeatherMonitor MetOcean software receives temperature
measurement data at 1Hz.

Wet
Air Temperature:

A
parameter calculated[2]
from the measured Dry Air Temperature and measured Humidity parameters: the
lowest temperature that can be reached by the evaporation of water only. It
is the temperature felt by wet skin exposed to freely moving air. Wet Air
Temperature is less than or equal to the Dry Air Temperature.

Dew
Point:

A
parameter calculated[3]
from the measured Dry Air Temperature and Humidity parameters. Dew Point
Temperature is the temperature at which moisture or dew will form on surfaces
and in the air. Mist or fog is likely to form when Dew Point is near the Dry
Air Temperature. Dew Point will always be less than or equal to Wet Air
Temperature.

Humidity:

Humidity
is the measurement of the amount of water vapour in the air, measured as a
percentage. As Humidity approaches 100%, the air becomes fully saturated and
water vapour condenses and can produce cloud, mist or fog.

Wind
Chill Temperature:

Wind
Chill, sometimes known as Wind Chill Factor, is a
calculated[4]
value: the perceived air temperature of exposed skin due to the flow of cold
air. This can be a useful parameter in identifying conditions that add risk
to outdoor working.Note that Windchill Temperature is only defined for temperatures at
or below 10°C/50°F and wind speeds above 3 mph/ 5kmh.

Heat
stress:

A
parameter calculated[5]
from Dry Air Temperature and Humidity parameters, Heat Stress is a unitless
parameter that rates the human body’s ability to control its internal
temperature. For any Fugro GEOS MetOcean system, thresholds between
particular ranges of heat stress value can be configured in order to align
with local (Black/Red/Amber/Green) colour indications of this parameter.

The
numeric mean of barometric pressure measurements made at the elevation of the
defined pressure sensor during the measurement period. Unless otherwise
specified by the client, the Fugro GEOS WeatherMonitor MetOcean software
receives pressure measurements at 1Hz.

Mean
Sea Level Pressure (QNH):

A
function[6]
of Ambient Pressure and the elevation of the pressure sensor, QNH is a
calculated value of air pressure at mean sea level (MSL). The relationship
between QNH and barometric pressure is illustrated in figure 1. The term
‘QNH’ derives from the aviation Q-code for "Near Horizon" or
"No Height".

Helideck
Height Pressure (QFE):

A
function[7]
of Ambient Pressure, helideck elevation and pressure sensor elevation, QFE is
the calculated value of air pressure at the elevation of the helideck. The
relationship between QFE and barometric pressure is illustrated in figure 1.
The term ‘QFE’ derives from the Aviation Q-code for "Field
Elevation".

Notes:

One Hectopascal [hPa] is equivalent to One Millibar [mb]. Other units of
atmospheric pressure are Inches of Mercury (InHg). The Fugro GEOS
WeatherMonitor system provides pressure data in hPa unless specified
otherwise by a client.

A MetOcean system deployed to a
vessel or platform with a variable draft will include the functionality for
the elevation of the pressure sensor and helideck location to be adjusted
according to draft. Where draft information is provided to the Fugro GEOS
system in real time, this is accomplished automatically. Alternatively, the
system user can enter the current vessel or platform draft through a password
protected data entry box within the system data display webpages.

Diagram:

QFE

QFE correction factor

Sensor elevation

QNH correction factor

QNH

Relationship
between elevation and barometric pressure values for a semisubmersible
platform

This is a calculated (rather than directly measured) parameter, and is derived
from a spectral analysis of the data and is defined as 4 * SQR(M0) where M0
is the zeroth moment. It can also be defined as 4 times the standard
deviation of the sea surface variation (trough to crest) over the measurement
period and is approximately equal to the average wave height of the 1/3
highest waves.

Maximum
Wave Height (Hmax):

This
parameter is defined as the crest to succeeding trough measurement of the
largest individual wave within the preceding measurement period.

Wave
Crest Height
(Hcrest):

The
height of the largest wave crest within the measurement period, measured from
the mean of all sea levels measured within the preceding measurement period.

Diagram

Hmax

Hs

Hcrest

Wave height Parameters

Significant
Wave Period (Tz):

This
is a calculated (rather than directly measured) parameter, and is derived
from a spectral analysis of the data and is defined as SQR(M0/ M+2).
It is sometimes known as the mean wave period.

Peak
Wave Period (Tp):

This
is a calculated (rather than directly measured) parameter, and is derived
from a spectral analysis of the data and is defined as (M-2 * M+1)
/ (M0 * M0). An alternative definition of Tpeak is that
it is 1/Fp where Fp is the peak of the spectra i.e. the Frequency at which the
maximum energy occurs

Diagram

Tz

Tp

Wave Time Periods

Wave
direction

This depends on the sensor being
used to acquire measurements, but is usually defined as the average direction
of all incident waves. Angles are measured as waves coming from the
stated bearing.

Notes:

Unless
specified otherwise by a client, a Fugro GEOS WeatherMonitor system with a
downwards looking radar ranging sensor uses wave analysis calculations
defined by the Shell Oil technical note TS211. A system configured to this
standard processes 4096 measurements made at 2Hz (34min 8sec). Note:
Calculations are repeated after each subsequent acquisition of 120
measurements (60 seconds), not a true one-for-one fifo of values.
The
application of SWAP (Standard Wave Analysis Program) wave analysis is
possible, according to client specifications. This method of wave analysis
provides data fields as per those described above, but this data analysis
method provides individual output parameters according to waves in each of
several time-period categories. The SWAP method was derived from the original
specification set by the Rijkswaterstaat Monitoring Network Infrastructure by
the Oceanographic Company of the Netherlands (OCN). Fugro GEOS can provide
further details if required (contact Venturer | .support@fugro.com)
Other
wave analysis engines categorise waves in to two divisions, according to
their time period. Longer time period waves are referred to as "swell" waves
and shorter time period waves are referred to as "wind" waves. Swell is
normally caused by distant storms or other wind systems: due to this swell is
more stable in its direction and frequency than ‘normal’ waves caused by the
wind. The time period boundary between wind and swell waves is not fixed, but
varies, being determined from a combination of wave and wind data[8].
When
the measured Significant Wave Height (Hs) is below approximately
0.3m, the Fugro GEOS HMS/Met system will show the word "Calm"
against wave parameters measured from downwards-looking radar units. It is
not possible to calculate wave parameters with acceptable accuracy in such
still conditions.

Measurement
methods

Wave
data within Fugro GEOS MetOcean monitoring systems can be derived from a
variety of measurement sources. It is most common to use a downwards looking
radar ranging sensor to monitor the sea surface. This method provides
accurate wave parameters, irrespective of weather conditions, but cannot
provide wave direction measurements. The Fugro GEOS WeatherMonitor
application can interface to directional wave measurement buoys to provide
wave direction information. Some Fugro GEOS MetOcean systems provide wave
direction information from an x-band scanning radar based wave analysis
system, based on image processing techniques. Contact Fugro GEOS for further
technical details of this measurement method if required.

Spectral
wave data

When
specified, Fugro GEOS MetOcean systems with wave measurement functionality
can provide wave data analysed within defied divisions in the wave-frequency
domain. This is referred to as the provision of spectral wave data. Depending
on customer requirements, spectral wave data may be plotted as an
Frequency/Energy X/Y plot based on the previous calculation period of data,
or may be periodically provided as tabular numeric data within formatted text
data files.

This
is the smallest distance between the lowest working level of an offshore
installation (often referred to as the Cellar Deck) and the sea surface over
the last wave measurement period. It is derived from the fixed dimensions of
the installation and the parameter Hcrest. For floating systems
where draft information is provided to the Fugro GEOS system in real time,
the air gap calculations accommodate changing draft. For other floating
systems, the system user can enter the current vessel or platform draft
through a password protected data entry box within the system data display
webpages in order that air gap data is correct.

Tide
Level:

This
value is the mean height of the sea surface over the last wave measurement
period with respect to the long term mean water level.
Depending
on customer requirements, systems may also present tidal predictions, extracted from almanac data for the required location.

Extreme
Level:

The
highest individual sea surface height over the last wave measurement period
with respect to the long term mean water level. This parameter differs from Hcrest
which is a measurement with respect to the mean water level identified
within the wave measurement period.

This
parameter reports the average current speed at the depth indicated. Current
data is usually presented as an average of measurements made in a non-rolling
10 minute window. This parameter is corrected for vessel course, speed,
motion and heading in the case of moving or floating systems

Current
Direction:

The
average direction in which the measured current is flowing. Current direction
is shown as ‘towards’ and is presented with the associated depth (below the
water surface) of the measured value. Current direction is usually presented
as an average of measurements made in a non-rolling 10 minute window. This
parameter is corrected for vessel course, speed, motion and heading in the
case of moving or floating systems

Depth:

The
depth of water in which current speed and direction measurements are taken.
Depth values reference the sea surface as the origin, increasing in value
towards the sea bed. The initial configuration of the current meter element
of a MetOcean monitoring system

Current
Profile:

This
data is usually presented as a plot of Depth (Y axis) versus Current Speed
and/or Current Direction. This plot shows the variability of current speeds
and/or directions throughout the monitored water column.

Current
Time Series:

This
is a plot showing the variation of either measured current speed or current direction
with time for a specific water depth.

Notes

It is usual to use Acoustic Doppler sensors for current measurements. Dependent on the specific system requirements, such sensors may be seabed, buoy, or near-surface mounted. Antifoul precautions and appropriate maintenance to elimiate biofouling from acoustic transducers is important in order to maintain the quality of reported data.

The
height of the lowest cloud layer above long term mean water level. It is
usual to present this parameter in the non-SI units of feet.

Cloud
Base 2:

The
height of the bottom of the second distinct cloud layer above long term mean
water level. It is usual to present this parameter in the non-SI units of
feet.

Cloud
Base 3:

The
height of the bottom of the third distinct cloud layer above long term mean
water level. It is usual to present this parameter in the non-SI units of
feet.

Notes

Cloud base heights are
measured using an eye-safe pulsed radar system. Such systems are configured
to point nominally vertically, but may be adjusted to eliminate direct
incident sunlight in near-equatorial applications. Different instruments
identify cloud bases using different signal processing, but a rule of thumb
is that a cloud base exists at an altitude where the horizontal visibility is
1000m or less. Measurements reported by an instrument relate to the sky
directly above.

This
parameter, sometimes referred to as Meteorological Optical Range, or MOR, is
the distance over which the intensity of a light beam is attenuated to 5% of
the original intensity. This measurement is usually presented in units of
metres, and is calculated by measuring the amount of infra-red scatter in a
small volume of air at the sensor location and assuming this sample has
similar properties to the surrounding air mass. Contaminants in the air at
the sensor location will lower the inferred visibility.

Present
Weather

Reported
Present Weather is a calculated category derived from precipitation,
visibility and temperature measurements. These three independent measurements
together provide sufficiently data for an accurate evaluation of prevailing
weather type. This parameter is presented as a category, either in United
States National Weather Service (NWS) or World Meteorological Organization
(WMO) code formats.

Heave
is the linear vertical (up/down) motion of a vessel or platform. It is
measured as a real-time displacement in metres from a calculated centre
position. Note that the heave at one location on a rigid vessel or platform
will not be the same as the heave at another location if there is any element
of rotational (pitch or roll) motion.

Total
heave

This
parameter reports the total maximum vertical displacement within the specified
(rolling) measurement window – the difference between the highest and lowest
recorded elevations within the measurement duration.

Heave
Period:

The
heave period is defined as the time taken for the vessel or platform to
execute one complete cycle of vertical movement (oscillation) from the upper
and lower points of the vertical motion. It is calculated from identifying
the zero crossing points of the heave measurements. The Fugro GEOS
WeatherMonitor system software calculates heave period based on the time
between successive motion zero-upcrossings identified in motion data at a 2Hz
sampling rate. The quantity of motion data used within the calculation is
either 1, 10 or 20 minutes, and this duration is identified against any web
page data displays. For HCA compliant systems, the heave period data
displayed on the main helideck monitoring page is based on a motion data
sample of 20 minutes.

Heave
Rate (calculated)

This
is a calculated parameter, the numeric mean of the ratio of heave amplitude
to cycle time, when dividing the vertical motion of the measured system in to
sequential oscillation cycles

Heave
Rate (measured)

This is a measured parameter, reported directly by a motion sensing instrument. It is an instantaneous representation of the z-velocity of the motion sensor at the point of reporting.

Maximum
Average Heave Rate (MAHR)

This
is a calculated parameter, the ratio of (Maximum Heave in the measurement
period) to (half the mean heave period in the measurement period) and has
units of ms-2

Pitch:

This
measured parameter reports the rotation of a floating object around a
port-starboard axis. It is usual for positive pitch to refer to the condition
where the bow of a vessel or the forward face of a platform moves "up".
Pitch is usually presented in units of degrees, and the measured value
applies equally at all locations around a rigid system.

Roll:

Rolling
involves side-to-side movement of the vessel. The rolling period is defined
as the time taken for a full rolling oscillation from the horizontal to the
left, back to horizontal then to the right and then back to horizontal. Roll
is measured in degrees. Positive roll occurs when the elevation of the
starboard side of a vessel or installation decreases, ie "port-up"

Surge:

The
backward and forward movement of the vessel. Positive values are forward and
negative values are backward. Surge is measured in metres.

Sway:

The
Port and Starboard movement of the vessel. Positive values are to Port and
negative values are to Starboard. Sway is measured in metres.

Inclination

Inclination
angle is the parameter used to report the maximum tilt of the vessel or
system. It is calculated from both pitch and roll angles. The angle of
maximum inclination is not reported.

Heave
compensation

This
term relates to the use of heave measurements at the location of a downwards
looking wave radar ranging unit, to compensate radar-to-water-surface
measurements for vertical motion (heave) of the radar sensor unit.

Lever
arm offset heave

As
noted in the section "heave" above, the heave at one location on a rigid
vessel or platform will not be the same as the heave at another location if
there is any element of rotational (pitch or roll) motion.
Lever
arm offset heave is the term used when a mathematical function is applied to
the heave, pitch and roll measured at one point on a rigid body, to determine
the heave at another point on the same rigid body.
This
calculation can be used, for example, to calculate the heave at the location
of a radar ranging sensor from the motion measurements made at a motion
sensor mounted to the vessel or system’s helideck.

Significant Heave Rate (SHR)

This parameter is specified within the scope of UK-North sea helideck monitoring systems as twice the RMS of heave rate measurements in the preceding 20 minute window. In order to ensure that this is accurately represented, the sampling rate of heave rate should be ≥2Hz

Motion Severity Index (MSI)

This parameter is specified within the scope of UK-North sea helideck monitoring systems.
It represents the ratio of helideck accelerations in the horizontal and vertical axes as a unitless number, and is defined as follows: - where xdotdot, ydotdot, and zdotdot are the instantaneous accelerations of the helideck in each of the three axes.

"Due to accuracy requirements on the acceleration
measurements the motion sensing equipment has to be mounted directly under
the helideck centre. Alternatively the motion sensing equipment can be
mounted in the accommodation below the helideck within a maximum distance of
4 meters from the helideck centre. If a longer distance is used the MSI
calculation will be affected."

Measured
as the amount of rainfall falling in a fixed time interval. It is measured in
mm min-1. This unit of (depth per unit time) is frequently
referred to as rainfall, but is more accurately described as rain intensity,
or rainfall rate. Data presented within the Fugro GEOS WeatherMonitor
application is matched to client requirements, but often a 10 minute rolling
sum of the rain intensity and a 1 hour rolling sum of rain intensity are
presented and recorded. Dependent on client requirements, rainfall can be
measured by means of the disdrometer function within a present weather
detection instrument, or by means of a dedicated rain-gauge instrument.
Measurements from a present weather instrument require scaling by a factor
which can be determined by means of the rainfall collected within a WMO
standard collection vessel. This scaling will usually be completed by a Fugro
GEOS engineer at the point of commissioning of a deployed WeatherMonitor
system.

Solar
Energy:

This
is measured by an instrument called a pyranometer which measures the amount
of solar energy incident on the sensor. Solar energy is measured in units Wm‑2.
Any inclination of a pyranometer’s sensitive surface away from the direction of
incident sunlight directly impacts the measurements. According to client
requirements, the output from a pyranometer can also be used to determine
poor lighting conditions of an outside work area, an accepted contributing
factor to workplace accidents.

When
this function is requested and implemented, the Fugro GEOS WeatherMonitor
system publishes data through an OPC server hosted as part of the
WeatherMonitor system. The most recent measured parameters, and associated
tags (unique strings to identify each variable) are held by the OPC server,
which must be interrogated by an OPC client in order to provide data. Data
transfer is instigated by the client.
A
deployed Fugro GEOS WeatherMonitor system, hosts the MetOcean parameters
defined by the client against tag names provided by the client. It is usual
at the point of Factory or Site acceptance testing, to validate the correct
operation of the OPC server by using an OPC client application (OPC Explorer)
to verify that the correct values are "available".
The
Fugro GEOS WeatherMonitor OPC server implementation is compliant with version
2.05a of the OPC specification. A standard configuration will update the data
held by the OPC server on a 1 minute interval.

Modbus

The Weather Monitor system can output data in MODBUS
format either using TCP/IP (Preferred Output) or Serial Connectivity.
The MODBUS system can either be a MODBUS MASTER (unusual but possible) OR (more normally) a
MODBUS SLAVE system
Our MODBUS system complies with version V1.1b3 of the specifications produced by the MODBUS Organisation
Fugro GEOS can provide
further details if required (contact Venturer | .support@fugro.com)

NMEA

When
specified, the Fugro GEOS WeatherMonitor application can generate standard or
so-called "vendor-specific" NMEA0183 sentences populated with realtime data
as specified.
The
WeatherMonitor application can output NMEA sentences to any connected serial
(COM) port, or as a TCP/IP client running on a client defined port on the
localhost.
NMEA
sentences can be output at any frequency between XXX and YYY. Note that if
the requirement for custom NMEA sentences exceeds the maximum length defined
within the NMEA0183 specification, the maximum output frequency can be
reduced.
The
Fugro GEOS WeatherMonitor application generates and appends the NMEA sentence
checksum for each generated sentence.

Text
file

The Weather Monitor System can generate
standard ASCII TEXT files of comma separated values at prgrammable intervals. These files can be written
to any location accessible from the Host PC. The Values in the file can be any of the parameters currently
being measured. The Text file can be formatted in different ways and Fugro GEOS can provide
further details if required (contact Venturer | .support@fugro.com)

Text
file (FTP)

Any of the TEXT files created by
the Weather Monitor System can be sent via in built basic FTP system.
Fugro GEOS can provide further details if required (contact Venturer | .support@fugro.com)

Relay

An external relay system can be installed
to control external devices or provide alarm signals. A variety of options exist for normally open or normally closed
relays and the system can be supplied to control 4 or 8 relays in one unit. A high power unit can be used
to enable AC voltages of 5 Amps at 250 volts to be switched.
Fugro GEOS can provide further details if required (contact Venturer | .support@fugro.com)

XML

Weather Monitor can be configured to send data
at regular intervals using the XML protocol. This system is used for clients who wish to display data on our
UK Hosted server FugroWeather.
Fugro GEOS can providefurther details if required (contact Venturer | .support@fugro.com)

METAR

A Metar is a standard meteorological message normally sent at hourly or 3 hourly intervals.
It consists of a coded summary of the local meteorological conditions and is used for aircraft operations.
The Fugro GEOS Weather Monitor System can generate standard metar messages in accordance with WMO FM15-XII specification
(as ammended).
Fugro GEOS can provide further details if required (contact Venturer | .support@fugro.com)

MANMAR
FM13

The Weather Monitor System can generate a MANMAR Outputas specified by the Canadian Government.
This is based on the WMO FM13-X specification.
Fugro GEOS can provide further details if required (contact Venturer | .support@fugro.com)

A number of deployed systems aquire anchor-chain tension measurements either from Fugro GEOS supplied instrumentation or from client's third party systems. A Fugro GEOS WeatherMonitor system allows simultaneous monitoring of chain tensions with relevant metocean parameters such as wind, wave and current data.

Excursion monitoring

For movable installations, it can be useful to graphically plot installation position information as an X/Y plot against a target location. Some Fugro GEOS systems present position data in this way alongside anchor tension measurements.

Using the
calculation – Measured Speed*(1/ ((Wind
Sensor Height/10)^0.1255)) following the agreement reached by the North Sea
Meteorological Panel of the UK Met Office. Note that the exponent 0.1255 reflects surface roughness and atmospheric stability. The value is referred to as the Wind Shear Exponent, and is approximated to 0.13 for UK-CAA specified helideck monitoring systems.

The
computation of the heat index is a refinement of a result obtained by multiple
regression analysis carried out by Lans P. Rothfusz and described in the 1990
National Weather Service (NWS) Technical Attachment (SR 90-23)